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Fine Structure of the Gas Bladder of Alligator Gar, Atractosteus Spatula Ahmad Omar-Ali1, Wes Baumgartner2, Peter J

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Fine Structure of the Gas Bladder of Alligator Gar, Atractosteus Spatula Ahmad Omar-Ali1, Wes Baumgartner2, Peter J www.symbiosisonline.org Symbiosis www.symbiosisonlinepublishing.com International Journal of Scientific Research in Environmental Science and Toxicology Research Article Open Access Fine Structure of the Gas Bladder of Alligator Gar, Atractosteus spatula Ahmad Omar-Ali1, Wes Baumgartner2, Peter J. Allen3, Lora Petrie-Hanson1* 1Department of Basic Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS 39762, USA 2Department of Pathobiology and Population Medicine, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS 39762, USA 3Department of Wildlife, Fisheries and Aquaculture, College of Forest Resources, Mississippi State University, Mississippi State, MS 39762, USA Received: 1 November, 2016; Accepted: 2 December, 2016 ; Published: 12 December, 2016 *Corresponding author: Lora Petrie-Hanson, Associate Professor, College of Veterinary Medicine, 240 Wise Center Drive PO Box 6100, Mississippi State, MS 39762, USA, Tel: +1-(601)-325-1291; Fax: +1-(662)325-1031; E-mail: [email protected] Lepisosteidae includes the genera Atractosteus and Lepisosteus. Abstract Atractosteus includes A. spatula (alligator gar), A. tristoechus Anthropogenic factors seriously affect water quality and (Cuban gar), and A. tropicus (tropical gar), while Lepisosteus includes L. oculatus (spotted gar), L. osseus (long nose gar), L. in the Mississippi River and the coastal estuaries. Alligator gar platostomus (short nose gar), and L. platyrhincus (Florida gar) (adversely affect fish )populations. inhabits these Agricultural waters andrun-off is impactedaccumulates by Atractosteus spatula [2,6,7]. Atractosteus are distinguishable from Lepisosteus by agricultural pollution, petrochemical contaminants and oil spills. shorter, more numerous gill rakers and a more prominent accessory organ. The gas bladder, or Air Breathing Organ (ABO) of second row of teeth in the upper jaw [2]. Atractosteus spatula alligatorThese fish gar are (Atractosteus bimodal air spatulabreathers,), is and a vascularized use a primitive air sac lung located as an are distributed in lakes, rivers and estuaries along the coast of dorsal to the body lumen. It has characteristics of amphibian lungs. the northern Gulf of Mexico [3,8,9]. Currently, estimated gar respiratory exchange with aerial gas exchange. The alligator gar gas alligator gar numbers have decreased [5]. bladderAlligator is gar an air-breathingelongated air organssac that function originates to dorsalsupplement to the branchial pharynx. numbers and fishing regulations vary by state. In Louisiana, their aquatic habitats range from desert to tropical rain forest. Air enters through a pharyngeal-esophageal duct that is controlled by 5mm long and is lined by ciliated columnar epithelium that is AmphibiansAir breathing evolved fishes to breatheoccur in air fresh while and inhabiting salt water aquatic [1] and or continuoustwo glottal ridges.with the The central pharyngeo-esophageal canal epithelium. duct The isgas approximately bladder has a central canal that subdivides the bladder into right and left lobes. Each lobe is further divided by septa into series of air spaces. The evolved to breathe by exchanging gases from the water and the terrestrial environments. In contrast, bimodal air breathing fish septa consist of blood vessels and smooth and striated muscles. Air circulates throughout the central canal, lobes and air spaces. The thickness of the septa is determined by underlying, supportive atmosphere [1], while inhabiting water. Obligatory air breathing striated muscle. The internal surface of the gas bladder is a continuous obligatoryfishes use onlyair breathers aerial gas can exchange utilize branchial and bimodal and Airair Breathingbreathing respiratory epithelial layer that includes mucus cells, pneumocytes, fishes use primarily aerial gas exchange [10-13]. Bimodal and and ciliated epithelial cells. An understanding of the normal tissue characteristics of this air breathing organ provides a baseline for Organ (ABO) respiration simultaneously [1]. Gars are bimodal air studying the effects of environmental toxins on this organ. breathing fish that use their gas bladder as a respiratory organ Keywords: Alligator gar; Atractosteus spatula; Air breathing into extractdirect contactoxygen fromwith thethe atmosphereenvironment. [1], They especially have inimportant hypoxic functionsenvironments including [14]. Fishrespiration, gills have ion a large regulation, surface areaexcretion and areof organ, Gas bladder; Pharyngeo-esophageal duct Introduction nitrogenous waste, and gas exchange [15-18]. Gill surface areas Alligator gar, Atractosteus spatula, is member of the and lamellar thickness are reduced in air breathing fishes in comparison to non-air breathing fishes, but still function for is phylogenetically placed between the chondrosteans and both O2 uptake and most of CO2 excretion [19-22]. Infraclass Holostei. This group includes primitive fish and amphibianThe gas lungs bladder function of airsimilarly, breathing these fish two hasorgans histological develop the teleosts [1]. Holostei arose around 180 million years ago ontogeneticallyfeatures of amphibian from lungsdifferent [23,24]. tissues Although [25]. theEmbryologically, fish ABO and [2,3], and includes the orders Amiiformes, the bowfin, and TheLepisosteiformes, alligator gar theis the gars. largest These fishof the have gars not (nearlybeen well 3 studiedmeters as a dorsal diverticulum of the esophagus and is joined to the maximally)[4]. Gars occur [5]. in Within North andthe orderCentral Lepisosteiformes, America, as well asthe in family Cuba. esophagusthe gas bladder by the originates pneumatic from duct the pharyngeo-esophageal[26,27]. This duct remains area Symbiosis Group *Corresponding author email: [email protected] Fine Structure of the Gas Bladder of Alligator Gar, Atractosteus Spatula Copyright: © 2016 Omar-Ali, et al. were hydroxide, rinsed again in deionized water, dehydrated through surroundingin fish with a the physostomous presence or air absence bladder, of buta pneumatic is absent induct adult in graded then alcohol, rinsed stained in deionized with hematoxylin water, dipped and in eosin, 0.3% andammonia cover fish with a physoclistic air bladder [28]. There is controversy numerous septa that provide a large vascularized area for gas lepisosteid fish (reviewed in [29]. The bladder itself contains Pictureslipped. Frame™ Slides software.were viewed under light microscopy on an Olympus BX 51 (Olympus America Inc.) and photographed using muscle throughout the gas bladder. It is attached to the body Transmission Electron Microscopy (TEM) wallexchange by dorsal [30]. retractors, There is allowingalso abundant for contraction. smooth and skeletal Most studies on the physiology of gars have utilized Lepisosteus Samples were primarily fixed in 2% glutaraldehyde in the bladder in oxygen uptake and carbon dioxide release and cacodylate buffer (0.1 M phosphate buffer, pH 7.2) and then post species [1,30]. Such studies confirm the function of fixed in 2% osmium tetroxide at 4°C. Samples were dehydrated functions and presumably physiology are seen in Atractosteus in solutions of increasing ethanol concentration from 35% spatulaits necessity when fish are in hypoxic waters [1,14,22]. Similar to 100% ETOH, and then in solutions of increasing acetone concentration. Finally, samples were embedded in Spurr’s resin. Alligator[1,31]. gar is exposed to petrochemical pollutants and Ultra-sections were made from each block using a Reichert Jung agricultural runoff because of the environments they inhabit. sectionsultra-microtome [35,36]. andAll sectionsstained withwere toluidine viewed underblue stain transmission for thick Furthermore, as top predators they can bio accumulate sections or uranyl acetate and lead citrate for the ultra-thin pollutants. Alligator gar were evaluated in our studies following Resultselectron microscopy on a JEOL JEM-1230 at 80 kV. structure of the alligator gar air breathing organ has not been Gross Morphology documented.the Gulf of Mexico The purposeoil spill [32,33].Toof this study our was knowledge, to histologically the fine describe the alligator gar ABO using light and electron The alligator gar gas bladder is a large, dorsoventrally microscopy. Knowledge of this organ is necessary to evaluate the effects of pollutants on alligator gar. The ABO is the focus of musculoskeletal tissues of the dorsal coelom along its entire flattened, elongate organ that is intimately associated with the Materialsour on-going and studies Methods of this unusual fish. length and width (Figure1 A, G). The bladder originates at the abrupt termination of the pharyngeo-esophageal duct (Figure Animals collagenous folds that run along its entire length on either side of1D, the asterisks) vertebral and column, is attached blending to the into body the wall stroma by paired that slenderinvests the aorta and cardinal veins associated with the mesonephros Nine alligator gar were obtained from the Private John Allen width of the body, tapering and terminating at the end of the National Fish Hatchery in Tupelo, MS, and held in fresh water (Figure 1G). The width of the gas bladder is proportional to the at the Mississippi Agriculture and Forestry Experiment Station, South Farm Aquaculture Unit, following published methods coelom (Figure 1 A, B). [34].When sampled, the fish weighed 318 to 320 gm and pharynx between the epi pharyngeal teeth, extending caudally to the Thejunction pharyngeo-esophageal
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